Eleven Senate Democrats called on President Obama to make a final decision on the Keystone XL pipeline by May 31. / Pablo Martinez Monsivais, AP

by Aamer Madhani, USA TODAY

by Aamer Madhani, USA TODAY

The White House on Thursday rejected a push by 11 Senate Democrats - including several facing tough reelection fights in November - for President Obama to make a final decision on whether to approve the the Keystone XL pipeline by May 31.

The lawmakers made their case for a "definitive timeline" in a letter to Obama on Thursday. They called on the president to use his executive authority to approve TransCanada's permit application for the pipeline that would deliver oil from the tar sands of northwest Canada to the Gulf Coast.

"Our position on that process hasn't changed, which is that it needs to run its appropriate course without interference from the White House or Congress," White House press secretary Jay Carney told reporters. "So that review continues at the State Department where it's housed in accordance with past practice of previous administrations of both parties. And when there's a decision to be announced, it will be announced."

The lawmakers who signed the letter are Mary Landrieu of Louisiana, Heidi Heitkamp of North Dakota, Mark Begich of Alaska, Joe Donnelly of Indiana, Kay Hagan of North Carolina, Joe Manchin of West Virginia, Claire McCaskill of Missouri, Mark Pryor of Arkansas, Jon Tester and John Walsh, both of Montana, and Mark Warner of Virginia.

Landrieu, Begich, Hagan, Pryor and Walsh are all expected to face tough contests in November, as Democrats try to cling to control of the Senate. All 11 senators who signed the letter are established backers of the pipeline, which environmental activists say would have a devastating impact on the climate if it were built.

"We need a definitive timeline laid out, a timeline that reduces the comment period for federal agencies, officials and other entities," the senators wrote to Obama. "We cannot miss another construction season."

The State Department issued an environmental impact statement on the project earlier this year in which it concluded the pipeline will have a negligible impact on climate because expanded development of carbon-heavy tar sands in northwest Canada is inevitable, with or without the pipeline. Obama has said that climate impact would weigh heavily in his decision whether to approve or reject the pipeline.

Obama is awaiting a recommendation on the pipeline from State, which is in the midst of a 90-day review.

Oklahoma Gov. Mary Fallin, a Republican, said Obama told her and other governors at a White House meeting in February that he expected to come to a final decision on the pipeline "in a couple of months."